Nowadays, the transport sector is one of the main sources of greenhouse gas (GHG) emissions and air pollution in cities. The use of renewable energies is therefore imperative to improve the environmental sustainability of this sector. In this regard, biofuels play an important role as they can be blended directly with fossil fuels and used in traditional vehicles’ engines. Bioethanol is the most used biofuel worldwide and can replace gasoline or form different gasoline-ethanol blends. Additionally, it is an important building block to obtain different high added-value compounds (e.g., acetaldehyde, ethylene, 1,3-butadiene, ethyl acetate). Today, bioethanol is mainly produced from food crops (first-generation (1G) biofuels), and a transition to the production of the so-called advanced ethanol (obtained from lignocellulosic feedstocks, non-food crops, or industrial waste and residue streams) is needed to meet sustainability criteria and to have a better GHG balance. This work gives an overview of the current production, use, and regulation rules of bioethanol as a fuel, as well as the advanced processes and the co-products that can be produced together with bioethanol in a biorefinery context. Special attention is given to the opportunities for making a sustainable transition from bioethanol 1G to advanced bioethanol.

The present work reviews the role of biogas as advanced biofuel in the renewable energy system, summarizing the main raw materials used for biogas production and the most common technologies for biogas upgrading and delving into emerging biological methanation processes. In addition, it provides a description of current European legislative framework and the potential biomethane business models as well as the main biogas production issues to be addressed to fully deploy these upgrading technologies. Biomethane could be competitive due to negative or zero waste feedstock prices, and competitive to fossil fuels in the transport sector and power generation if upgrading technologies become cheaper and environmentally sustainable.

Olive tree crops, extensively cultivated in Southern European countries, yield large amounts of olive tree pruning (OTP) biomass. This could be used within the framework of a bio-based economy that maximizes the utilization of biomass resources in a sustainable way. In the present work, the techno-economic feasibility of an OTP-based integrated biorefinery is evaluated by the process simulation software Aspen Plus, while the process is aimed at the production of ethanol, xylitol, antioxidants and electricity. Overall, the proposed plant could perform economically, and it is self-sufficient from an energy resource point of view. The plant as designed yields around 109 l of ethanol, 27 kg of xylitol and 43 kg of antioxidants per ton of OTP biomass, with an estimated production cost of 0.24 € l⁻¹, 1.48 € kg⁻¹ and 5.12 € kg⁻¹, respectively. In a 10-year period, the economic profitability of the biorefinery plant is within a positive investment balance, with a net present value (NPV) of 32.1 M€ and a payback period of 5–6 years. These figures point out the opportunities for placing in the market several OTP-based products. Based on these data, the construction of small-scale OTP-based lignocellulosic biorefineries seems to be a realistic scenario.

The aim of this work was to evaluate the economic feasibility of the bioethanol production (BEP) based on olive tree pruning (OTP) as a biomass feedstock with optimization of the dilute acid pretreatment in focus. For this, the BEP was simulated taking into account the influence of the operating conditions of the pretreatment stage. Then, the techno-economic results were analyzed by means of the response surface methodology (RSM). The results show that lowest price of BE was 1.94 USD l⁻¹ with a yield of 174.12 l t⁻¹ OTP under optimal conditions. As a conclusion, the raw material cost has a strong influence in the economic feasibility of the BEP from OTP. The inclusion of other processing lines into the process would improve the process economy.

Intensive horticultural systems for the production of vegetables in greenhouses represent one of the main industries generating organic waste, as those that do not meet the quality standards for the fresh market or the processing industry are discarded. This highlights the importance of using these residues as raw material for other applications, such as bioenergy and bioproducts production, within the framework of a bio-based economy that maximizes the utilization of biomass resources in a sustainable manner. In this work, the microbial oil production from discarded pepper using the oleaginous yeast Cryptococcus curvatus was evaluated. Overall, a total lipid accumulation of 16.8 g/L was achieved with a fatty acid profile suitable to produce biodiesel. The lipid yield obtained was 0.12 g/g sugars. In addition, experimental results were used to assess the techno-economic feasibility of a proposed microbial oil plant using the software Aspen Plus. This plant yields approximately 96 kg of microbial oils/ton dry discarded pepper, with an estimated Minimum Selling Price of 7 €·kg⁻¹. These figures point out the necessity of increasing the yield of microbial oil production and considering the utilization of possible by-products, such as mannitol and cell debris, to improve the economic performance of the process.